David Arora in Mushrooms Demystified (Ten Speed Press) describes
Agaricus argenteus as a grass-loving species similar to Agaricus
cupreobrunneus (brown field mushroom) and Agaricus campestris.
It is a common edible species in the southern United States.
Paul F Hamlyn
NW Fungus Group, UK
http://ourworld.compuserve.com/homepages/pfh2/nwfg.htm